Early neuromyelitis optica antibody-induced molecular changes in aquaporin 4 and associated proteins at astrocyte endfeet in murine brain tissues

Neuromyelitis optica spectrum disorder (NMOSD) is characterized by the production of autoantibodies against aquaporin 4 (AQP4). Because NMOSD progressively causes irreversible and severe neurological damages, understanding the initial molecular changes induced by anti-AQP4 antibody binding is crucial for designing early interventions. However, knowledge about the effects of the antibodies before AQP4 loss in brain tissues is limited. Using acutely prepared mouse brain slices, we aimed to investigate the initial molecular impact of NMO model antibodies on AQP4 and its associated proteins. We employed two different types of NMO model antibodies, E5415A and E5415B; E5415A recognizes both M1 and M23 isoforms, whereas E5415B exclusively binds to M23. We found that E5415A but not E5415B disrupted the uniform perivascular localization of AQP4, leading to fragmentation. We further addressed the impact of these changes on AQP4-associated proteins and found that strong colocalizations between AQP4 and dystrophin-glycoprotein complex (DGC) components were preserved, even after AQP4 localization pattern became fragmented. Thus, our study reveals the initial molecular changes in the AQP4 channel at the astrocytic endfeet in response to NMO model antibodies and highlights the early pathological events occurring in NMOSD.